Semiconductor wafer washing system and method of supplying chemicals to the washing tanks of the system

ABSTRACT

A semiconductor wafer washing system can execute a method in which the washing solution is quickly changed over and over again without the need to alter the structure of the system. The wafer washing system includes a washing solution supply section in which a plurality of chemicals are stored separately, and from which selected ones of the chemicals can be supplied in a predetermined ratio into a washing tank. A circulation section includes circulation piping connected to the washing tank for circulating the washing solution to and from the tank. A discharge section selectively discharges residual chemicals or washing solution from the washing solution supply section, the washing tank and the circulation section. A controller controls the flow of chemicals and washing solution in the washing solution supply section, the circulation section and the discharge section, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 11/038,127, filed Jan. 19,2005, which is a divisional of application Ser. No. 09/956,459, filedSep. 20, 2001, now U.S. Pat. No. 6,863,079, issued Mar. 8, 2005, whichis incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the washing of semiconductor wafers toremove impurities or particles from the wafers during the manufacturingof semiconductor devices. More particularly, the present inventionrelates to a semiconductor wafer washing system and to a method ofsupplying chemicals to the washing tanks thereof to produce a washingsolution.

2. Description of the Related Art

Semiconductor devices are generally made by forming at least one circuitpattern on a wafer through repeated and selected processes such asphotoresist patterning, etching, washing, diffusion, and metaldeposition processes. The washing process is performed to remove varioustypes of particles and impurities that have been produced during theprevious processes so that such particles and impurities do not affectthe subsequent processes. For instance, the etching away of a patternedphotoresist can produce particles of polymer. The wafer is washed afterthe etching process to remove the particles.

The density, quantity, and temperature of the washing solution must beestablished and controlled on the basis of various parameters, such asthe manufacturing processes involved, the type of wafer, and the like.To meet such requirements, the washing apparatus has various kinds ofsensors, including an optical sensor, to provide feedback for thecontrol of the chemical characteristics, the quantity and temperature ofthe washing solution, etc. The general structure and operation of aconventional washing apparatus will now be described with reference toFIGS. 1 and 2.

A plurality of wafers W are transferred with a cassette K to theapparatus (ST10) where they are positioned in a loading zone 10 (ST12).Then, the cassette K and wafers W are transferred to an aligner 12 inwhich the wafers are arranged (ST14) with their flat zones (not shown)aligned at a reference position in the cassette. Subsequently, thecassette K and the wafers W are transferred to a first transfer station16 by a transfer device 14 (ST16).

The first transfer station 16 confirms the number of the wafers W (ST18)and, at the same time, transfers the wafers from the cassette K (ST20)to a robot 18 having a robot chuck (ST22). The cassette K is thentransferred by the transfer device 14 to a stand-by area 20 and, after apredetermined period of time, is placed at a second transfer station 26(ST24)(ST26). The wafers are then successively transferred by the robot18 into a plurality of washing tanks 22 containing washing solution(ST28).

The wafers W are submerged in the washing solution by the robot so thatimpurities on the wafers W are washed away by the washing solution. Thewafers W are then transferred by the robot 18 to a drying station 24where the wafers W are dried (ST30). The wafers W are then transferredby the robot 18 to the second transfer station 26. The second transferstation 26 arranges the wafers W again and confirms whether the samenumber of wafers W that arrived at the first transfer station 16 haveundergone the washing process (ST32).

The cassette K is transferred from the stand-by area 20 to the secondtransfer station 26 prior to the arrival of the wafers W. The secondtransfer station 26 loads the wafers W back onto the cassette K that hasbeen so transferred from the stand-by area 20 to the second transferstation 26 (ST34). In this way, the wafers W and cassette K arecontinuously unloaded and transferred to a position in preparation forthe next process (ST36).

As was mentioned previously, the conditions of the washing solution ineach of the washing tanks 22, i.e., the concentration, quantity,temperature, etc. must be maintained constant according to the type ofwafer W or process that dictates the need for cleaning the wafers W.Accordingly, when a new type of wafer is to be washed, a new type ofwashing solution must be used. It is difficult to create newenvironments that facilitate the cleaning of new types of wafers withnew cleaning solutions. In addition, the old type of washing solutionmust be discharged out of the system regardless of the remaining usefullife thereof, and the washing tanks 22 and washing solution supply 28must be thoroughly cleaned before they are to accommodate the new typeof washing solution. This process of changing the washing solutionrequires a lot of time.

In addition, the process also suffers from inefficiency because effortmust be spent in converting the apparatus to provide for the new washingsolution conditions. For instance, the new washing conditions mayrequire additional washing tanks 22 to be provided in the washingapparatus. Due to space considerations, this sometimes requires theremoval of existing elements, including the washing tanks 22, from theapparatus and the addition of completely new washing elements. Changingthe existing tanks also requires a lot of time.

As an alternative to modifying the washing apparatus, a completely newwashing system may be provided in the production line. However, this mayrequire reducing the size of the existing line or the new washing systemmight be just too large to incorporate into the existing line. Inaddition, fabricating and installing a completely new washing system ismuch more expensive in terms of material and labor than merely modifyingthe existing washing system.

As is also apparent from the description above, the elements of thewashing apparatus are arranged in line so that the wafers can be cleanedin a continuous operation. As shown in FIG. 3, the washing solution,which comprises a mixture of chemicals, is supplied to the washing tanks22 through a pipeline of a washing solution supply 28. The efficacy ofthe washing solution is reduced as the washing solution undergoeschemical reactions with the impurities on the wafers W. Therefore, thewashing solution is discharged out of the system after a predeterminedperiod of time so that pure washing solution can be introduced into thetanks 22. Nonetheless, it is difficult to maintain the requiredconcentration of the washing solution even when a plurality of washingtanks is provided.

Moreover, the period of refreshing the washing solution is relativelyshort. Thus, the conventional method suffers from a drawback in terms ofthe costs associated with the amount of washing solution that must beused.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor waferwashing system and method by which washing solution can be changedand/or the washing solution can be conditioned in a short period of timewithout altering the basic structure and arrangement of the existingwashing tanks.

Another object of the present invention is to provide a semiconductorwafer washing system and method by which the washing solution can beconserved, whereby the system is environmentally friendly and economicalto use.

Still another object of the present invention is provide a semiconductorwafer washing system and method by which the washing tanks can beflushed in such a way as to quickly facilitate the use of a new form ofwashing solution.

In order to accomplish these objects, the washing system according tothe present invention comprises a washing solution supply section thatincludes a plurality of chemical storage tanks in which a plurality ofchemicals are stored, respectively, and supply piping connected to thechemical storage tanks, a washing tank that receives the chemicals fromthe washing solution supply section via the supply piping, and adischarge section having a drain and discharge piping that allowsresidual chemicals and/or washing solution to be discharged from variousparts of the system to the drain. The washing system may also comprise acirculation section and a washing solution storage section. Thecirculation section includes circulation piping connected to the washingtank and through which piping washing solution is circulated from andback to the tank to enhance the mixing of the chemicals constituting thewashing solution. The washing solution storage section has one or morewashing solution storage tanks connected to the washing tank andcirculation piping for storing washing solution used to replenish and/orflush the washing tank and circulation piping.

Furthermore, each of the sections of the semiconductor washing systemincludes flow control means for controlling the flow of chemicals orwashing solution. A controller is operatively connected to the flowcontrol means of each section of the system so as to issue controlsignals that regulate the flow of the chemicals or washing solution toand from the sections of the system as conditions warrant. Thecontroller may comprise a central processing unit (CPU) or individualprocessing units provided in the sections of the semiconductor washingsystem, respectively.

For instance, the flow control means of the washing solution supplysection comprises flow control valves disposed in the supply piping. Thecontroller controls the flow control means of the washing solutionsupply section such that selected ones of the chemicals are supplied tothe washing tank in a predetermined ratio. Likewise, the flow controlmeans of the discharge section may comprise flow control valves disposedin the discharge piping. The controller controls these flow controlvalves such that washing solution is discharged from the washing tank invarious instances. On the other hand, the flow control means of thecirculation section comprises a variable output pump and/or a flowcontrol valve disposed in the circulation piping. Also, a pressure gaugemay be provided for monitoring the pressure of the washing fluid flowingthrough the circulation piping so that the pump may be feed-backcontrolled by the controller. The flow control means of the washingsolution storage section comprises a purge gas supply system forintroducing purge gas into the at least one washing solution storagetank and/or a variable output pump to force washing solution from thewashing solution storage tank(s) into the washing tank and circulationpiping. A flow control valve of the purge gas supply system and/or thepump is/are controlled by the controller.

In addition to enhancing the mixing of the chemicals constituting thewashing solution, the circulation section is used to condition thewashing solution. To this end, one or more filters are provided in thecirculation piping for filtering impurities from the washing solution.In addition, a heat exchanger is provided in a heat-exchangingrelationship with the circulation piping so that the washing solutioncan be maintained at a desired temperature.

Preferably, the washing solution supply section also includes aquantitative supply part for mixing precise amounts of the chemicalstogether before the chemicals are dispensed to the washing tank. Thequantitative supply part includes at least one mixing tub connected tothe washing tank, a cover covering the mixing tub so as to form a mixingtank therewith, a level sensor for sensing the level of chemicals in thetub and issuing a signal indicative of the level of chemicals in the tubto the controller, and a purge gas supply system for introducing purgegas into the covered tub and/or a variable output pump for forcing themixture of chemicals from the mixing tub and into the washing tank.

In this case, the flow control means of the discharge section includeselements associated with the quantitative supply part. Specifically, theflow control means of the discharge section will comprise a dischargeguide pipe(s) extending into the mixing tub, and driving means forraising and lowering the discharge guide pipe(s) such that an endthereof is positionable at a desired level within the mixing tub. Thedriving means may be any known linear driving mechanism appropriate formoving the guide pipe between two end limit positions and keeping theguide pipe temporarily fixed in place at the desired position, inresponse to a signal issued by the controller on the basis ofinformation received from the level sensor.

In order to accomplish the above-mentioned objects of the presentinvention, the semiconductor wafer washing method includes steps ofsupplying chemicals from respective ones of the chemical storage tanksinto the washing tank in a predetermined ratio to produce an originalwashing solution in the washing tank, circulating the washing solutionfrom a supplementary part of the washing tank back into a main part ofthe washing tank to facilitate the mixing of the chemicals constitutingthe washing solution, subsequently submerging semiconductor wafers intothe washing solution in the washing tank to thereby wash the wafers, anddraining washing solution circulating from the supplementary part of thewashing tank back to the main part of the washing tank.

The supplying of the chemicals from the chemical tanks into the washingtank can be carried out with an enhanced degree of precision by usingthe quantitative supply part as follows. The chemicals are firstsupplied at rates regulated by the controller into the mixing tank.During this time, the level of the chemicals in the mixing tank ismeasured and the flow of chemicals from the mixing tank to the washingtank is cut off. The end(s) of the discharge guide pipe(s) arepositioned in the mixing tank, and once the level of the chemicals inthe mixing tank exceeds a predetermined level, the discharge guidepipe(s) is/are opened to the drain. Accordingly, pressure in the mixingtank created by purge gas discharges an excess of the mixture ofchemicals from the mixing tank through the discharge guide pipe and tothe drain. Then, the mixture of chemicals is allowed to flow from themixing tank to the washing tank.

As was mentioned above, as the washing solution is being circulated fromthe supplementary part of the washing tank back to the main part of thewashing tank, the washing solution is conditioned. The washing solutionis filtered and the temperature of the washing solution is adjusted, ifnecessary.

Manufacturing requirements may dictate that a new form of the washingsolution be used to wash a batch of wafers. In this case, the originalwashing solution is drawn from the washing tank into a washing solutionstorage tank after the first batch of wafers have been washed.Subsequently, chemicals from respective ones of the chemical storagetanks are supplied into the main part of the washing tank in a new ratioto produce a new form of washing solution in the washing tank.Alternatively, the new form of washing solution can be taken fromanother one of the washing solution storage tanks, if such washingsolution has, for example, already been produced by the washing solutionsupply section and has been (used and then) stored.

In addition, the washing tank and the circulation piping should beflushed prior to introducing a new form of the washing solution into thewashing tank, to thereby eliminate remnants of the original washingsolution that would otherwise alter the composition of or otherwisecontaminate the new washing solution. Basically, this process entailssupplying a cleaning washing solution into the washing tank after theoriginal washing solution has been drawn into the washing solutionstorage tank and before the chemicals constituting the new form ofwashing solution have been supplied into the washing tank. Then, thecleaning washing solution is circulated between the main andsupplementary parts of the washing tank to thereby clean the washingtank. Finally, the cleaning washing solution is drained.

The cleaning washing solution can come from one of the washing storagesolution tanks. Alternatively, the cleaning washing solution can comedirectly from the chemical storage tanks. In either of these cases it ismost effective if the cleaning washing solution has the same compositionas the new washing solution that is to be used next. In any case, thewashing solution that is drained in the course of its circulating fromthe supplementary part of the washing tank back to the main part of thewashing tank is temporarily stored. The temporarily stored washingsolution is then diluted and discharged from the system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional washing apparatus;

FIG. 2 is a flow chart of the operation of the washing apparatus shownin FIG. 1;

FIG. 3 is a schematic diagram of a washing system of the conventionalapparatus;

FIG. 4 is a schematic diagram of one embodiment of a washing system ofsemiconductor wafer washing apparatus according to the presentinvention;

FIG. 5 is a schematic diagram of another embodiment of a washing systemof semiconductor wafer washing apparatus according to the presentinvention; and

FIG. 6 is a schematic diagram of part of the washing solution supplysection of the system of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to FIGS. 4through 6.

Basically, the semiconductor wafer washing system includes a washingsolution supply section 30 that stores each of the various chemicalsmaking up the washing solution and controls the flow rate of thechemicals, a washing tank 32 that receives the chemicals from thewashing solution supply section 30 and mixes the chemicals to make awashing solution used to wash the wafers W, a circulation section 34 forcirculating the washing solution through the tank 32, and a dischargesection 36 that discharges the residual chemicals and washing solutionfrom the system.

The washing tank 32 consists of a main part A, and a supplementary partB partitioned from one another. The washing solution is stored in themain part A as the solution is being mixed with chemicals supplied fromthe washing solution supply part 30, and the wafers W are cleaned in themain part A in the solution. The supplementary part B contains excesswashing solution overflowing from the main part A.

The circulation section 34 is connected to the washing tank 32 tocirculate the washing solution through the main part A and supplementarypart B of the washing tank 32. The circulation section 34 thus serves tomaintain the desired characteristics of the washing solution.

The discharge section 36 is directly connected to the supply section 30,the washing tank 32 and the circulation section 34 to selectivelydischarge from the system the washing solution or residual chemicalsfrom the supply section 30, washing tank 32, and circulation section 34.

The operation of the washing solution supply section 30, circulationsection 34, and discharge section 36 are is controlled by a controller100.

The structure of the semiconductor wafer washing system will beexplained in more detail below.

The washing solution supply section 30 comprises a plurality of chemicalstorage tanks 38 containing the chemicals, respectively, that are tomake up the washing solution. At least one of the chemicals is purewater or a diluent for diluting the other chemicals or for preventinghardening. Each of the chemical storage tanks 38 is connected to thewashing tank 32 through supply piping provided therein with at least oneflow control valve V. The piping may consist of main supply pipes S, ormain and branch supply pipes S, S=. A filter 40 for filtering thechemicals may be provided in any of the pipes. The filter 40 isconnected to a discharge pipe D through which a portion of the chemicalsor impurities filtered by the filter 40 is discharged from the system.

A flowmeter 42 is also provided in each of the supply pipes. Each flowmeter 42 measures the flow rate of the chemical flowing through the pipeand outputs a signal indicative of the flow rate to the controller. Thecontroller, in turn, controls the flow control valves V to maintain adesired flow rate of the chemicals. The flow rate of most of thechemicals can be controlled to some extent by the flow control valves V.However, the controlling of the flow rate of some exceptional chemicalsor an accurate mixing of some chemicals might require the use ofdiscrete quantitative supply apparatus 44 connected to the supply pipingS, S=, as shown in FIG. 5.

The quantitative supply apparatus 44 includes a quantitative mixing tank46 connected to a chemical storage tank 38 via piping. A level sensor 48is provided in the quantitative mixing tank 46 for measuring the amountof chemicals within the tank. The level sensor 48 also outputs a signal,indicative of the amount of chemicals within the tank 46, to thecontroller. The controller controls the flow control valves V in thepiping connected to the quantitative mixing tank 46, thereby controllingthe rate at which the chemicals flow into the tank 46.

The chemicals are typically volatile and so would evaporate if exposedto air. Hence, a cover 50 is detachably mounted to the quantitativemixing tank 46 so as to cover the tank 46 and thereby prevent areduction in the quality of chemicals in the tank 46 that wouldotherwise be caused by evaporation. In addition, a source of purge gasthat does not react with air, e.g. a nitride gas, is connected to thequantitative mixing tank 46 through the cover 50 by purge gas supplypiping 52.

The quantitative supply apparatus 44 may also include a pump 54 providedin-line with the supply piping S, S′ to pump the chemicals from thequantitative mixing tank 46 to the washing tank 32. The pump 54 ispreferably a variable speed pump connected to the controller so as togenerate a selected pressure in response to signals from the controller.Alternatively, the chemicals can be forced from the quantitative mixingtank 46 to the washing tank 32 by pressure generated by the purge gassupplied into the tank 46 through the purge gas supply piping 52.

In addition, the quantitative supply apparatus 44 should be connected tothe discharge section 36 so that any excessive amount of chemicals canbe drained from the tank 46. To this end, the discharge section 36 maycomprise a first (discharge guide) drain pipe 56 extending through thecover 50 of the quantitative tank 46. The drain pipe 56 is movable upand down (FIG. 6) by a driving mechanism so that the end thereof that islocated in the tank 46 may be repositioned. The end of the drain pipe 56is set by the driving mechanism at a level corresponding to the desiredlevel of chemicals in the tank 46, i.e., to regulate the amount ofchemicals in the tank. When an excessive amount of chemicals are presentin the tank 46, the flow of chemicals from the chemical tanks 38 to thewashing tank 32 via the quantitative mixing tank 46 is cut off. In thisstate, the excess chemicals in the tank 46 are forced through the drainpipe 56 and to the drain of the discharge section 36 by pressure in thetank 46 generated by purge gas supplied to the tank 46 through the purgegas supply piping 52.

The discharge section 36 may also include a second (discharge guide)drain pipe 58 that extends through the bottom of the quantitative tank46 and is connected to the drain of the discharge section 36. The seconddrain pipe 58 is also movable up and down by a driving mechanism. In theoperational state that prevents the chemicals from flowing from thechemical tanks 38 to the washing tank 32 via the quantitative tank 46,excess chemicals in the quantitative tank 46 can be drained through thesecond drain pipe 58 by the purge gas.

The first and second drain pipes 56, 58 may be selectively used or maybe used at the same time to drain chemicals from the tank 46. Inaddition, a pump may be provided in the first and second drain pipes 56,58 to force the chemicals therethrough.

The circulation section 34, as shown in FIG. 4 or 5, includescirculation piping R through which the mixture of washing solution iscirculated between the main part A and supplementary part B of thewashing tank 32. At least one flow control valve V is provided in thecirculation piping R for controlling the flow of the washing solutiontherethrough in response to a signal issued by the controller. Also, atleast one filter 40 is provided in the circulation piping R forfiltering impurities from the washing solution.

The circulation section 34 also includes a variable speed pump 54 thatoperates in response to a signal issued by the controller, and apressure gauge 62 for measuring the pressure of the washing solution andoutputting a signal indicative of the pressure to the controller. Acheck valve 64 in the circulation piping R discharges the washingsolution to the discharge part 36 through discharge piping D as long asthe pressure of the washing solution does not exceed a certainpredetermined pressure.

In addition, the circulation section 34 may include a heat exchanger 60operatively associated with the circulation piping R such that thetemperature of the washing solution flowing through the piping R ismaintained constant.

The circulation section 34 serves to condition the washing solution,e.g., to provide the correct composition and temperature. To this end,the chemicals supplied from the washing solution supply section 30 aremixed in the course of being introduced into the main part A of thewashing tank 32 to form the washing solution. Excess washing solutionoverflows into the supplementary part B from the main part A. Thecontroller opens the flow control valve V in the circulation piping R,and at the same time signals the pump 54 to operate, whereby the washingsolution in the supplementary part B is re-circulated to the main partA.

During this time, impurities or chemicals that harden the washingsolution are filtered from the washing solution by the filter 40. Thepressure of the washing solution produced by the pump 54 is monitored bythe pressure gage 62. The signals output by the pressure gage 62 to thecontroller are used to control the operation of the pump 54, whereby thepressure of the washing solution is kept within a predetermined range.

Note, the washing solution is discharged through the discharge piping Dof the discharge section 36 until the pump 54 starts operating andproduces a sufficient pressure.

The aforementioned operation is carried out until the chemicals aresufficiently mixed and the washing solution attains a certaintemperature, whereupon the wafers W are submerged in the washingsolution in the washing tank 32.

The discharge section 36 also includes at least one drain tub 66, anddischarge piping D′. The residual washing solution is stored in the atleast one drain tub 66 and is discharged therefrom through a pipe of thedischarge piping D. A supply pipe S extends into the tub 66 from thechemical storage tank 38 in which pure water or diluent is stored. Whenthe washing solution stored in the drain tub 66 starts to harden, thecontroller opens the valve V in the supply pipe extending into the tub66 from the chemical storage tank 38 in which pure water or diluent isstored, thereby preventing the discharge piping D from being cloggedwith chemical precipitate of the hardened washing solution. Another pipeof the discharge piping D branches from the circulation piping R suchthat washing solution can be discharged from the circulation section 34.The discharge piping D is provided with valves V that are controlled bythe controller to selectively discharge the washing solution from thecirculation section 34.

As shown in FIG. 5, the semiconductor wafer washing system may alsoinclude a washing solution storage section 70, connected to the washingtank 32 and circulation section 34, for selectively storing washingsolution having a predetermined composition. The storage section 70includes at least one storage tank 72, connection piping C that allowsthe washing solution stored in the tank 72 to be reintroduced into thecirculation piping R, and a valve(s) V provided in the connection pipingC for controlling the flow of washing solution in response to a signalfrom the controller.

The storage section 70 may also comprise means for creating pressure bywhich the washing solution is forced from the tank 72. The means may bea source of purge gas, such as N₂, and a purge gas supply pipe 52connected to the storage tank 72 and/or a variable speed pump 54provided in the connecting pipe C. The controller controls the flow ofthe purge gas into the storage tank 72 to produce a certain amount ofpressure therein, and controls the pump 54 as well, to thereby regulatethe flow of the stored washing solution from the tank 72 and through theconnection pipe C. The purge gas supply and the pump 54 may be operatedtogether or individually by the controller.

The washing solution storage section 70 stores washing solution that canbe used when new or other wafers W require new conditions to be cleanedunder.

As described above, in the semiconductor wafer washing system accordingto the present invention, a plurality of chemicals are separately storedin each of the chemical storage tanks 38. The chemicals are supplied tothe main part A of the washing tank 32 via elements such as the flowcontrol valves V and/or quantitative mixing tank 46.

When the chemicals are supplied via the quantitative mixing tank 46, thefirst and second discharge guide pipes 56, 58 are placed atpredetermined positions in response to signal issued by the controller.In addition, pressure is created in the quantitative mixing tank 46 bythe purge gas supply and which pressure is regulated by the controller.Still further, at least some of the chemicals are filtered by the filter40 provided in the supply piping before the chemicals are supplied tothe washing tank 32.

Thus, the chemicals are mixed together in a predetermined ratio to formthe washing solution. An excess amount of the washing solution in themain part A overflows into the supplementary part B, and the excess orresidual solution is re-circulated back to the main part A via therecirculation section 34 to further enhance the mixing of the chemicalsconstituting the washing solution and so that the solution can beconditioned, e.g. temperature-conditioned, if necessary.

The controller also serves to control the flow control means of thecirculation section so that the washing solution contained in thesupplementary part B of the washing tank 32 is re-supplied to the mainpart A of the tank. At the same time, the washing solution is purifiedby filter 40, and is heated/cooled by heat exchanger 60. The program ofthe controller is designed so that the chemicals constituting thewashing solution will be mixed and conditioned, e.g maintained at agiven constant temperature, in accordance with the washing needs of thewafers W that are to be cleaned in the main part A of the washing tank32.

Also, the controller serves to control the pressure of the washingsolution flowing through the circulation piping R of the circulationsection 34 so that the flow of the washing solution is stabilized andthe pressure is appropriate for the operation of the filters 40. Thepressure gauge 62 serves to measure the pressure in the section of thecirculation piping R extending between the filters 40. If the pressurebecomes excessive such as occurs when the filter(s) 40 become clogged,the check valve 64 opens allowing the washing solution to be discharged.That is, the check valve 64 allows the need to exchange the elements ofthe filters 40 to be determined.

The above-described discharge section 36 serves to temporally store (inthe drain tub 66) the residual chemicals, washing solution, orimpurities that are discharged from the washing solution supply section30 and the circulation section 34. The residual chemicals, washingsolution, or impurities are mixed (diluted) in the discharge sectionwith a predetermined amount of pure water or other diluent whereuponthey are discharged from the system through the discharge piping D anddrain.

Now, after semiconductor wafers have been washed in the main part A ofthe washing tank under the operation outlined above, it may be necessaryto wash other wafers using a different form of the washing solution. Inthis case, the washing solution is drawn from the washing tank 32 andcirculation piping R through the connection piping C and into a washingsolution storage tank 72. Subsequently, the controller controls the flowcontrol means, e.g. valves V, of the washing solution supply section 30such that the chemical(s) appropriate for washing the new wafers W arewithdrawn form the respective chemical storage tank(s) 38 and aresupplied to the washing tank 32. An operation similar to that describedabove is carried out to produce a new washing solution, i.e., to createthe new environment for washing the next wafers.

However, before these next wafers are actually washed, and after the oldwashing solution has been stored in the washing solution storage tank72, some of the new washing solution is supplied to and circulatedthrough the washing tank 32 and circulation section 34 for apredetermined period of time. Then, this portion of the new washingsolution is discharged. That is, the new washing solution contaminatedby the remnants of the old washing solution existing in the system isdischarged so that the system is clean before the new washing solutionused to wash the new wafers is produced in the washing tank 32.

It may also be necessary to re-establish the original environment inwhich the first set of wafers were washed. In this case, the washingsolution stored in the washing solution storage tank 72 is used. Theother (new) washing solution is drawn from the washing tank 32 andcirculation section 34 through a respective portion of the connectionpiping C and into another washing solution storage tank 72. Again,however, first chemicals are supplied form the washing solution supplysection 30 to the washing tank 32 in a predetermined ratio conforming tothat used to produce the original washing solution. This washingsolution is circulated through the washing tank 32 by the circulationsection for a predetermined period of time to clean the tank 32 andcirculation piping R. Then, the cleaning washing solution is dischargedso that the washing tank 32 and circulation section 34 remain free ofthe remnants of the new washing solution that was just used to washwafers.

Conversely, the cleaning washing solution may be the original washingsolution that was stored in the chemical storage tank 72. In this case,the original environment in which the first set of wafers were washed isre-established by supplying chemicals into the washing tank 32 from thewashing solution supply section 30 to thereby produce the second batchof original washing solution in the washing tank 32.

As an alternative to using the washing solution for cleaning, i.e.,flushing the system, as described above using either the chemicals fromthe washing solution supply section 30 or the washing solution from thestorage tank 70, the washing solution supply section 30 may include aseparate chemical storage tank 38 containing pure water or a separatewashing device dedicated to the cleaning of the washing tank 32 andcirculation section 34.

According to the present invention, as described above, the environmentin which wafers are washed, i.e., the characteristics of the washingsolution, can be easily changed in a short period of time. On the otherhand, the characteristic of a particular washing solution can bemaintained over a particularly long washing cycle. Still further, littlewashing solution is wasted when having to switch back and forth betweenvarious kinds of washing solutions. The present invention can provideeach and all of these working advantages without the need to alter theset-up of the washing tanks. Accordingly, the present invention enhancesthe efficiency and reduces the costs currently associated with thewashing of semiconductor wafers during the process of manufacturingsemiconductor devices.

1. A method of producing semiconductor wafer washing solution during themanufacturing of semiconductor devices, said method comprising: storingchemicals, capable of constituting different forms of washing solution,separately in respective chemical storage tanks; providing a washingtank having a main part, and a supplementary part extending around andpartitioned from said main part; supplying chemicals from respectiveones of the chemical storage tanks into the main part of the washingtank in a predetermined ratio to produce an original washing solution inthe washing tank and until a portion of the washing solution overflowsthe main part of the washing tank into the supplementary part;circulating the washing solution that has flown into the supplementarypart of the washing tank back into the main part of the washing tank tofacilitate the mixing of the chemicals constituting the washingsolution; subsequently submerging semiconductor wafers into the washingsolution in the main part of the washing tank to thereby wash thewafers; and draining washing solution circulating from the supplementarypart of the washing tank back to the main part of the washing tank. 2.The method as defined in claim 1, wherein said supplying of thechemicals into the main part of the washing tank comprises measuring theflow rates of the chemicals, respectively, as the chemicals flow fromthe chemical storage tanks towards the main part of the washing tank,and regulating the flow of the chemicals based on the measured flowrates.
 3. The method as defined in claim 1, wherein said supplying ofthe chemicals into the main part comprises supplying the chemicals intoa mixing tank whereby the chemicals are mixed together, measuring thelevel of the mixture of chemicals in the mixing tank, and supplying themixture of chemicals from the mixing tank into the main part of thewashing tank once the chemicals supplied into the mixing tank rise to apredetermined level in the washing tank.
 4. The method as defined inclaim 3, wherein said supplying of the mixture of chemicals from themixing tank into the main part of the washing tank comprises introducingpurge gas into the mixing tank to pressurize the interior thereof. 5.The method as defined in claim 4, and further comprising cutting off theflow of the mixture of chemicals from the mixing tank to the washingtank, and positioning the end of a discharge guide pipe at apredetermined position in the top portion of the mixing tank, and whilethe flow of the mixture of chemicals from the mixing tank to the washingtank is cut off, opening the discharge guide pipe to a drain when thelevel of the chemicals in the tank exceeds said predetermined level,whereby pressure in the mixing tank created by the purge gas dischargesan excess of the mixture of chemicals from the mixing tank through thedischarge guide pipe and to the drain.
 6. The method as defined in claim3, and further comprising cutting off the flow of the mixture ofchemicals from the mixing tank to the washing tank, and positioning theend of a discharge guide pipe at a predetermined position in the bottomportion of the mixing tank, and while the flow of the mixture ofchemicals from the mixing tank to the washing tank is cut off, openingthe discharge pipe to a drain.
 7. The method as defined in claim 1, andfurther comprising filtering the washing solution circulating from thesupplementary part of the washing tank towards the main part of thewashing tank to remove impurities from the washing solution, andeffecting a heat exchange with the washing solution circulating from thesupplementary part of the washing tank towards the main part of thewashing tank to maintain the washing solution at a constant temperaturewhile the wafers are being washed.
 8. The method as defined in claim 7,wherein said circulating of the washing solution from the supplementarypart of the washing tank back to the main part of the washing tankcomprises measuring the pressure of the washing solution flowing fromthe supplementary part of the washing tank, and based on the measuredpressure, regulating the pressure of the washing solution that isflowing from the supplementary part of the washing tank back to the mainpart of the washing tank, and wherein said draining of the washingsolution circulating from the supplementary part of the washing tankback to the main part of the washing tank is carried out when thepressure of the washing solution flowing from the supplementary part ofthe washing tank exceeds a predetermined pressure.
 9. The method asdefined in claim 1, and further comprising drawing the original washingsolution from the washing tank into a washing solution storage tankafter the wafers have been washed, and subsequently supplying chemicalsfrom respective ones of the chemical storage tanks into the main part ofthe washing tank in a ratio different from said predetermined ratio toproduce a new form of washing solution in the washing tank.
 10. Themethod as defined in claim 9, and further comprising, after the originalwashing solution has been drawn into the washing solution storage tankand before the chemicals constituting the new form of washing solutionhave been supplied into the washing tank, supplying a cleaning washingsolution into the washing tank, circulating the cleaning washingsolution between the main and supplementary parts of the washing tank tothereby clean the washing tank, and then draining the cleaning washingsolution.
 11. The method as defined in claim 9, and further comprisingdrawing said new form of the washing solution from said washing tankinto another washing solution storage tank, supplying chemicals fromrespective ones of the chemical storage tanks into the main part of thewashing tank in said predetermined ratio to produce a cleaning washingsolution in the washing tank having the same characteristics as theoriginal washing solution that is stored in the washing solution storagetank, circulating the cleaning washing solution between the main andsupplementary parts of the washing tank to thereby clean the washingtank, subsequently draining the cleaning washing solution, and, afterthe washing tank is cleaned, drawing the original washing solution fromthe washing solution storage tank back into the washing tank.
 12. Themethod as defined in claim 9, and further comprising drawing said newform of the washing solution from said washing tank into another washingsolution storage tank, subsequently supplying the original washingsolution from the washing solution storage tank back into the washingtank to produce a cleaning washing solution in the washing tank,circulating the cleaning washing solution between the main andsupplementary parts of the washing tank to thereby clean the washingtank, subsequently draining the cleaning washing solution, and after thewashing tank is cleaned supplying chemicals from respective ones of thechemical storage tanks into the main part of the washing tank in saidpredetermined ratio to produce a second batch of washing solution in thewashing tank having the same characteristics as the original washingsolution.
 13. The method as defined in claim 1, and further comprisingtemporarily storing the washing solution drained in the course of itscirculating from the supplementary part of the washing tank back to themain part of the washing tank, diluting the temporarily stored washingsolution, and then discharging the diluted washing solution.